Metering rod control for an air valve carburetor

Abstract

An air valve for a carburetor has its lower end mounted for pivotal movement between open and closed positions relative to the air and fuel mixture conduit and carries a metering rod which extends generally in a horizontal direction. The metering rod has an end extending within a metering orifice of an orifice plate in an opening of the mixture conduit wall. The metering rod is urged by a coiled torsion spring upwardly against the orifice plate. The torsion spring has a small coil with a relatively high spring rate and a large coil with a relatively low spring rate. The large coil continuously urges the rod into engagement with the upper surface of the orifice plate defining the orifice, while the small coil urges the rod into engagement with the orifice plate only after the air valve is around one half open. The metering rod is mounted for limited pivotal movement relative to the air valve and the torsion spring exerts a generally uniform light force to the metering rod throughout the longitudinal movement of the metering rod to compensate for the varying distance between the orifice plate and pivotal mounting of the metering rod and the increased load against the rod caused by impinging air flow.

What is claimed is: 
     
       1. In a carburetor having an air and fuel mixture conduit, a throttle valve within the conduit, an air valve mounted across the conduit above the throttle valve and pivoted adjacent its lower end for movement between open and closed positions relative to the mixture conduit, a metering rod carried by the air valve and extending generally in a horizontal direction, an orifice plate in an opening in the wall of the mixture conduit having a metering orifice therein receiving the extending end of the metering rod, and means on the air valve mounting the metering rod for limited pivoted movement; the improvement comprising a torsion spring engaging the metering rod to urge the metering rod into contact with the side of the orifice, said torsion spring including two portions thereof which have different spring rates, one portion continuously urging the metering rod against the side of the orifice and the other portion urging the metering rod against the side of the orifice after the air valve has been at least partially opened.   
     
     
       2. In a carburetor as set forth in claim 1 wherein said portions of said torsion spring comprises a large diameter coil portion continuously exerting a torsion force against the metering rod and a small diameter coil portion exerting a torsion force against the metering rod only after the air valve has been partially opened, said large diameter coil portion providing a torsion force against the metering rod which increases constantly upon movement of the air valve from a closed position to an open position. 
     
     
       3. In a carburetor as set forth in claim 1 wherein said air valve comprises a pair of spaced generally vertically extending sides and a web connecting the sides having a central slot therein, pivot means mounting said metering rod within said central slot for limited pivotal movement about a generally horizontal axis relative to the air valve, said portions of said torsion spring comprising a pair of spaced coiled portions on opposite sides of the metering rod, said coiled portions being of different diameters to exert different spring forces against the metering rod to urge the metering rod against the side of the orifice. 
     
     
       4. In a carburetor as set forth in claim 3 wherein said sides each has an inwardly extending lug thereon, said lugs being in opposed spaced relation to each other and said pivot means being supported on said lugs with said metering rod mounted between said lugs for pivotal movement. 
     
     
       5. In a carburetor having an air and fuel mixture conduit, a throttle valve within the conduit, an air valve mounted across the conduit above the throttle valve and pivoted adjacent its lower end for movement between open and closed positions relative to the mixture conduit, a metering rod carried by the air valve and extending generally in a horizontal direction, and an orifice plate in an opening in the wall of the mixture conduit having a metering orifice therein receiving the extending end of the metering rod; the improvement comprising, spring means engaging the metering rod to urge the metering rod into contact with the side of the orifice, said spring means including two coiled portions thereof which have different spring rates, one coiled portion continuously urging the metering rod upwardly against the upper side of the orifice and the other coiled portion urging the metering rod upwardly against the side of the orifice after the air valve has been at least partially opened, both of said coiled portions exerting a force against the metering rod which after engagement with the metering rod increases constantly upon movement of the metering rod away from the orifice, and pivot means on the air valve mounting the metering rod for pivotal movement about a generally horizontal axis relative to the air valve.   
     
     
       6. In a carburetor as set forth in claim 5 wherein said air valve has a pair of spaced generally vertically extending sides, each side having an inwardly extending lug thereon, said lugs being in opposed spaced relation to each other, said pivot means being in opposed spaced relation to each other, said pivot means being supported on said lugs with said metering rod and said spring means being mounted between said lugs. 
     
     
       7. In a carburetor as set forth in claim 6 wherein said each of the coiled portions of the spring means is mounted adjacent an associated lug and each has a tang thereon fitting over a subjacent lug and contacting the associated lug for increasing the force exerted by the associated coiled portion exerted against the metering rod upon movement of the air valve toward an open position.